Merge rust-bitcoin#5256: Add an iterator that yields the bytes of an encoded object

b7cb088 Add iterator tests for EncodableByteIter (Mitchell Bagot)
4fa296a Add an iterator to yield the bytes of an encoded object (Mitchell Bagot)

Pull request description:

  The Encoder trait currently provides an iterator-style interface for objects to yield byte slices. Since other utilities, like hex::BytesToHexIter rely on byte-by-byte input to function, providing a method of yielding raw bytes for Encodables increases the versatility of the encoding on Encodable objects.
  
  Add EncodableByteIter struct to iterate the bytes from an Encodable as u8 values, and tests to demonstrate function alongside hex::BytesToHexIter
  
  Closes rust-bitcoin#5190


ACKs for top commit:
  apoelstra:
    ACK b7cb088; successfully ran local tests
  tcharding:
    ACK b7cb088


Tree-SHA512: f6cc2428ad0a452f17004b066799e33d401d83b4961ba85c806f84dc60238aa7d20f0c08c57571ca2ec3695a86e06d37e60e2b54dbba965218e1c9e396c8374c

Author: apoelstra

Cargo-minimal.lock

@@ -77,6 +77,7 @@ name = "bitcoin-consensus-encoding"
 version = "1.0.0-rc.2"
 dependencies = [
  "bitcoin-internals",
+ "hex-conservative 0.3.0",
 ]
 
 [[package]]

Cargo-recent.lock

@@ -76,6 +76,7 @@ name = "bitcoin-consensus-encoding"
 version = "1.0.0-rc.2"
 dependencies = [
  "bitcoin-internals",
+ "hex-conservative 0.3.0",
 ]
 
 [[package]]

api/consensus_encoding/all-features.txt

@@ -87,6 +87,14 @@ impl<'e, T> core::marker::Sync for bitcoin_consensus_encoding::SliceEncoder<'e,
 impl<'e, T> core::marker::Unpin for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Unpin
 impl<'e, T> core::panic::unwind_safe::RefUnwindSafe for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::RefUnwindSafe, T: core::panic::unwind_safe::RefUnwindSafe
 impl<'e, T> core::panic::unwind_safe::UnwindSafe for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::UnwindSafe, T: core::panic::unwind_safe::RefUnwindSafe
+impl<'s, T: bitcoin_consensus_encoding::Encodable + 's> bitcoin_consensus_encoding::EncodableByteIter<'s, T>
+impl<'s, T: bitcoin_consensus_encoding::Encodable + 's> core::iter::traits::iterator::Iterator for bitcoin_consensus_encoding::EncodableByteIter<'s, T>
+impl<'s, T> core::marker::Freeze for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Freeze
+impl<'s, T> core::marker::Send for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Send
+impl<'s, T> core::marker::Sync for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Sync
+impl<'s, T> core::marker::Unpin for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Unpin
+impl<'s, T> core::panic::unwind_safe::RefUnwindSafe for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::RefUnwindSafe
+impl<'s, T> core::panic::unwind_safe::UnwindSafe for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::UnwindSafe
 impl<'sl> bitcoin_consensus_encoding::BytesEncoder<'sl>
 impl<'sl> core::marker::Freeze for bitcoin_consensus_encoding::BytesEncoder<'sl>
 impl<'sl> core::marker::Send for bitcoin_consensus_encoding::BytesEncoder<'sl>
@@ -360,6 +368,8 @@ pub fn bitcoin_consensus_encoding::Decoder::end(self) -> core::result::Result<Se
 pub fn bitcoin_consensus_encoding::Decoder::push_bytes(&mut self, bytes: &mut &[u8]) -> core::result::Result<bool, Self::Error>
 pub fn bitcoin_consensus_encoding::Decoder::read_limit(&self) -> usize
 pub fn bitcoin_consensus_encoding::Encodable::encoder(&self) -> Self::Encoder
+pub fn bitcoin_consensus_encoding::EncodableByteIter<'s, T>::new(encodable: &'s T) -> Self
+pub fn bitcoin_consensus_encoding::EncodableByteIter<'s, T>::next(&mut self) -> core::option::Option<Self::Item>
 pub fn bitcoin_consensus_encoding::Encoder2<A, B>::advance(&mut self) -> bool
 pub fn bitcoin_consensus_encoding::Encoder2<A, B>::current_chunk(&self) -> &[u8]
 pub fn bitcoin_consensus_encoding::Encoder3<A, B, C>::advance(&mut self) -> bool
@@ -414,6 +424,7 @@ pub struct bitcoin_consensus_encoding::Decoder2<A, B> where A: bitcoin_consensus
 pub struct bitcoin_consensus_encoding::Decoder3<A, B, C> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder
 pub struct bitcoin_consensus_encoding::Decoder4<A, B, C, D> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder, D: bitcoin_consensus_encoding::Decoder
 pub struct bitcoin_consensus_encoding::Decoder6<A, B, C, D, E, F> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder, D: bitcoin_consensus_encoding::Decoder, E: bitcoin_consensus_encoding::Decoder, F: bitcoin_consensus_encoding::Decoder
+pub struct bitcoin_consensus_encoding::EncodableByteIter<'s, T: bitcoin_consensus_encoding::Encodable + 's>
 pub struct bitcoin_consensus_encoding::Encoder2<A, B>
 pub struct bitcoin_consensus_encoding::Encoder3<A, B, C>
 pub struct bitcoin_consensus_encoding::Encoder4<A, B, C, D>
@@ -445,5 +456,6 @@ pub type bitcoin_consensus_encoding::Decoder6<A, B, C, D, E, F>::Output = (<A as
 pub type bitcoin_consensus_encoding::Decoder::Error
 pub type bitcoin_consensus_encoding::Decoder::Output
 pub type bitcoin_consensus_encoding::Encodable::Encoder<'s> where Self: 's: bitcoin_consensus_encoding::Encoder
+pub type bitcoin_consensus_encoding::EncodableByteIter<'s, T>::Item = u8
 pub type bitcoin_consensus_encoding::VecDecoder<T>::Error = bitcoin_consensus_encoding::VecDecoderError<<<T as bitcoin_consensus_encoding::Decodable>::Decoder as bitcoin_consensus_encoding::Decoder>::Error>
 pub type bitcoin_consensus_encoding::VecDecoder<T>::Output = alloc::vec::Vec<T>

api/consensus_encoding/alloc-only.txt

@@ -83,6 +83,14 @@ impl<'e, T> core::marker::Sync for bitcoin_consensus_encoding::SliceEncoder<'e,
 impl<'e, T> core::marker::Unpin for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Unpin
 impl<'e, T> core::panic::unwind_safe::RefUnwindSafe for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::RefUnwindSafe, T: core::panic::unwind_safe::RefUnwindSafe
 impl<'e, T> core::panic::unwind_safe::UnwindSafe for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::UnwindSafe, T: core::panic::unwind_safe::RefUnwindSafe
+impl<'s, T: bitcoin_consensus_encoding::Encodable + 's> bitcoin_consensus_encoding::EncodableByteIter<'s, T>
+impl<'s, T: bitcoin_consensus_encoding::Encodable + 's> core::iter::traits::iterator::Iterator for bitcoin_consensus_encoding::EncodableByteIter<'s, T>
+impl<'s, T> core::marker::Freeze for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Freeze
+impl<'s, T> core::marker::Send for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Send
+impl<'s, T> core::marker::Sync for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Sync
+impl<'s, T> core::marker::Unpin for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Unpin
+impl<'s, T> core::panic::unwind_safe::RefUnwindSafe for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::RefUnwindSafe
+impl<'s, T> core::panic::unwind_safe::UnwindSafe for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::UnwindSafe
 impl<'sl> bitcoin_consensus_encoding::BytesEncoder<'sl>
 impl<'sl> core::marker::Freeze for bitcoin_consensus_encoding::BytesEncoder<'sl>
 impl<'sl> core::marker::Send for bitcoin_consensus_encoding::BytesEncoder<'sl>
@@ -333,6 +341,8 @@ pub fn bitcoin_consensus_encoding::Decoder::end(self) -> core::result::Result<Se
 pub fn bitcoin_consensus_encoding::Decoder::push_bytes(&mut self, bytes: &mut &[u8]) -> core::result::Result<bool, Self::Error>
 pub fn bitcoin_consensus_encoding::Decoder::read_limit(&self) -> usize
 pub fn bitcoin_consensus_encoding::Encodable::encoder(&self) -> Self::Encoder
+pub fn bitcoin_consensus_encoding::EncodableByteIter<'s, T>::new(encodable: &'s T) -> Self
+pub fn bitcoin_consensus_encoding::EncodableByteIter<'s, T>::next(&mut self) -> core::option::Option<Self::Item>
 pub fn bitcoin_consensus_encoding::Encoder2<A, B>::advance(&mut self) -> bool
 pub fn bitcoin_consensus_encoding::Encoder2<A, B>::current_chunk(&self) -> &[u8]
 pub fn bitcoin_consensus_encoding::Encoder3<A, B, C>::advance(&mut self) -> bool
@@ -379,6 +389,7 @@ pub struct bitcoin_consensus_encoding::Decoder2<A, B> where A: bitcoin_consensus
 pub struct bitcoin_consensus_encoding::Decoder3<A, B, C> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder
 pub struct bitcoin_consensus_encoding::Decoder4<A, B, C, D> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder, D: bitcoin_consensus_encoding::Decoder
 pub struct bitcoin_consensus_encoding::Decoder6<A, B, C, D, E, F> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder, D: bitcoin_consensus_encoding::Decoder, E: bitcoin_consensus_encoding::Decoder, F: bitcoin_consensus_encoding::Decoder
+pub struct bitcoin_consensus_encoding::EncodableByteIter<'s, T: bitcoin_consensus_encoding::Encodable + 's>
 pub struct bitcoin_consensus_encoding::Encoder2<A, B>
 pub struct bitcoin_consensus_encoding::Encoder3<A, B, C>
 pub struct bitcoin_consensus_encoding::Encoder4<A, B, C, D>
@@ -410,5 +421,6 @@ pub type bitcoin_consensus_encoding::Decoder6<A, B, C, D, E, F>::Output = (<A as
 pub type bitcoin_consensus_encoding::Decoder::Error
 pub type bitcoin_consensus_encoding::Decoder::Output
 pub type bitcoin_consensus_encoding::Encodable::Encoder<'s> where Self: 's: bitcoin_consensus_encoding::Encoder
+pub type bitcoin_consensus_encoding::EncodableByteIter<'s, T>::Item = u8
 pub type bitcoin_consensus_encoding::VecDecoder<T>::Error = bitcoin_consensus_encoding::VecDecoderError<<<T as bitcoin_consensus_encoding::Decodable>::Decoder as bitcoin_consensus_encoding::Decoder>::Error>
 pub type bitcoin_consensus_encoding::VecDecoder<T>::Output = alloc::vec::Vec<T>

api/consensus_encoding/no-features.txt

@@ -49,6 +49,14 @@ impl<'e, T> core::marker::Sync for bitcoin_consensus_encoding::SliceEncoder<'e,
 impl<'e, T> core::marker::Unpin for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Unpin
 impl<'e, T> core::panic::unwind_safe::RefUnwindSafe for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::RefUnwindSafe, T: core::panic::unwind_safe::RefUnwindSafe
 impl<'e, T> core::panic::unwind_safe::UnwindSafe for bitcoin_consensus_encoding::SliceEncoder<'e, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::UnwindSafe, T: core::panic::unwind_safe::RefUnwindSafe
+impl<'s, T: bitcoin_consensus_encoding::Encodable + 's> bitcoin_consensus_encoding::EncodableByteIter<'s, T>
+impl<'s, T: bitcoin_consensus_encoding::Encodable + 's> core::iter::traits::iterator::Iterator for bitcoin_consensus_encoding::EncodableByteIter<'s, T>
+impl<'s, T> core::marker::Freeze for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Freeze
+impl<'s, T> core::marker::Send for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Send
+impl<'s, T> core::marker::Sync for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Sync
+impl<'s, T> core::marker::Unpin for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::marker::Unpin
+impl<'s, T> core::panic::unwind_safe::RefUnwindSafe for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::RefUnwindSafe
+impl<'s, T> core::panic::unwind_safe::UnwindSafe for bitcoin_consensus_encoding::EncodableByteIter<'s, T> where <T as bitcoin_consensus_encoding::Encodable>::Encoder: core::panic::unwind_safe::UnwindSafe
 impl<'sl> bitcoin_consensus_encoding::BytesEncoder<'sl>
 impl<'sl> core::marker::Freeze for bitcoin_consensus_encoding::BytesEncoder<'sl>
 impl<'sl> core::marker::Send for bitcoin_consensus_encoding::BytesEncoder<'sl>
@@ -267,6 +275,8 @@ pub fn bitcoin_consensus_encoding::Decoder::end(self) -> core::result::Result<Se
 pub fn bitcoin_consensus_encoding::Decoder::push_bytes(&mut self, bytes: &mut &[u8]) -> core::result::Result<bool, Self::Error>
 pub fn bitcoin_consensus_encoding::Decoder::read_limit(&self) -> usize
 pub fn bitcoin_consensus_encoding::Encodable::encoder(&self) -> Self::Encoder
+pub fn bitcoin_consensus_encoding::EncodableByteIter<'s, T>::new(encodable: &'s T) -> Self
+pub fn bitcoin_consensus_encoding::EncodableByteIter<'s, T>::next(&mut self) -> core::option::Option<Self::Item>
 pub fn bitcoin_consensus_encoding::Encoder2<A, B>::advance(&mut self) -> bool
 pub fn bitcoin_consensus_encoding::Encoder2<A, B>::current_chunk(&self) -> &[u8]
 pub fn bitcoin_consensus_encoding::Encoder3<A, B, C>::advance(&mut self) -> bool
@@ -298,6 +308,7 @@ pub struct bitcoin_consensus_encoding::Decoder2<A, B> where A: bitcoin_consensus
 pub struct bitcoin_consensus_encoding::Decoder3<A, B, C> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder
 pub struct bitcoin_consensus_encoding::Decoder4<A, B, C, D> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder, D: bitcoin_consensus_encoding::Decoder
 pub struct bitcoin_consensus_encoding::Decoder6<A, B, C, D, E, F> where A: bitcoin_consensus_encoding::Decoder, B: bitcoin_consensus_encoding::Decoder, C: bitcoin_consensus_encoding::Decoder, D: bitcoin_consensus_encoding::Decoder, E: bitcoin_consensus_encoding::Decoder, F: bitcoin_consensus_encoding::Decoder
+pub struct bitcoin_consensus_encoding::EncodableByteIter<'s, T: bitcoin_consensus_encoding::Encodable + 's>
 pub struct bitcoin_consensus_encoding::Encoder2<A, B>
 pub struct bitcoin_consensus_encoding::Encoder3<A, B, C>
 pub struct bitcoin_consensus_encoding::Encoder4<A, B, C, D>
@@ -324,3 +335,4 @@ pub type bitcoin_consensus_encoding::Decoder6<A, B, C, D, E, F>::Output = (<A as
 pub type bitcoin_consensus_encoding::Decoder::Error
 pub type bitcoin_consensus_encoding::Decoder::Output
 pub type bitcoin_consensus_encoding::Encodable::Encoder<'s> where Self: 's: bitcoin_consensus_encoding::Encoder
+pub type bitcoin_consensus_encoding::EncodableByteIter<'s, T>::Item = u8

consensus_encoding/Cargo.toml

@@ -20,6 +20,9 @@ alloc = ["internals/alloc"]
 [dependencies]
 internals = { package = "bitcoin-internals", path = "../internals", version = "0.4.0" }
 
+[dev-dependencies]
+hex = { package = "hex-conservative", version = "0.3.0" }
+
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]

consensus_encoding/src/encode/encoders.rs

@@ -592,4 +592,20 @@ mod tests {
         assert!(!e.advance());
         assert!(e.current_chunk().is_empty());
     }
+
+    #[test]
+    fn iter_encoder() {
+        let test_array = TestArray([1u8, 2, 3, 4]);
+        let mut iter = crate::EncodableByteIter::new(&test_array);
+        let mut byte = iter.next().unwrap();
+        assert_eq!(byte, 1u8);
+        byte = iter.next().unwrap();
+        assert_eq!(byte, 2u8);
+        byte = iter.next().unwrap();
+        assert_eq!(byte, 3u8);
+        byte = iter.next().unwrap();
+        assert_eq!(byte, 4u8);
+        let none = iter.next();
+        assert_eq!(none, None);
+    }
 }

consensus_encoding/src/encode/mod.rs

@@ -64,6 +64,35 @@ macro_rules! encoder_newtype{
     }
 }
 
+/// Yields bytes from any [`Encodable`] instance.
+pub struct EncodableByteIter<'s, T: Encodable + 's> {
+    enc: T::Encoder<'s>,
+    position: usize,
+}
+
+impl<'s, T: Encodable + 's> EncodableByteIter<'s, T> {
+    /// Constructs a new byte iterator around a provided encodable.
+    pub fn new(encodable: &'s T) -> Self {
+        Self { enc: encodable.encoder(), position: 0 }
+    }
+}
+
+impl<'s, T: Encodable + 's> Iterator for EncodableByteIter<'s, T> {
+    type Item = u8;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if let Some(b) = self.enc.current_chunk().get(self.position) {
+                self.position += 1;
+                return Some(*b);
+            } else if !self.enc.advance() {
+                return None;
+            }
+            self.position = 0;
+        }
+    }
+}
+
 /// Encodes an object into a vector.
 #[cfg(feature = "alloc")]
 pub fn encode_to_vec<T>(object: &T) -> Vec<u8>

consensus_encoding/src/lib.rs

@@ -42,4 +42,4 @@ pub use self::encode::encoders::{
     ArrayEncoder, BytesEncoder, CompactSizeEncoder, Encoder2, Encoder3, Encoder4, Encoder6,
     SliceEncoder,
 };
-pub use self::encode::{Encodable, Encoder};
+pub use self::encode::{Encodable, Encoder, EncodableByteIter};

consensus_encoding/tests/iter.rs

@@ -0,0 +1,59 @@
+use hex::BytesToHexIter;
+
+use bitcoin_consensus_encoding::{Encodable, ArrayEncoder, Encoder2, EncodableByteIter};
+
+struct TestArray<const N: usize>([u8; N]);
+
+impl<const N: usize> Encodable for TestArray<N> {
+    type Encoder<'s>
+        = ArrayEncoder<N>
+    where
+        Self: 's;
+
+    fn encoder(&self) -> Self::Encoder<'_> { ArrayEncoder::without_length_prefix(self.0) }
+}
+
+struct TestCatArray<const N: usize, const M: usize>([u8; N], [u8; M]);
+
+impl<const N: usize, const M: usize> Encodable for TestCatArray<N, M> {
+    type Encoder<'s>
+        = Encoder2<ArrayEncoder<N>, ArrayEncoder<M>>
+    where
+        Self: 's;
+
+    fn encoder(&self) -> Self::Encoder<'_> { Encoder2::new(
+            ArrayEncoder::without_length_prefix(self.0),
+            ArrayEncoder::without_length_prefix(self.1),
+        )
+    }
+}
+
+#[test]
+fn hex_iter() {
+    let data = TestArray([255u8, 240, 9, 135]);
+    let byte_iter = EncodableByteIter::new(&data);
+    let mut iter = BytesToHexIter::new(byte_iter, hex::Case::Upper);
+
+    let expect_str = "FFF00987";
+    for byte in expect_str.chars() {
+        let iter_byte = iter.next().unwrap();
+        assert_eq!(iter_byte, byte);
+    }
+    let none = iter.next();
+    assert_eq!(none, None);
+}
+
+#[test]
+fn hex_iter_cat_encoder() {
+    let data = TestCatArray([222u8, 173], [190u8, 239]);
+    let byte_iter = EncodableByteIter::new(&data);
+    let mut iter = BytesToHexIter::new(byte_iter, hex::Case::Lower);
+
+    let expect_str = "deadbeef";
+    for byte in expect_str.chars() {
+        let iter_byte = iter.next().unwrap();
+        assert_eq!(iter_byte, byte);
+    }
+    let none = iter.next();
+    assert_eq!(none, None);
+}